1. Field of the Invention
The present invention relates to a cellular mobile telecommunications system, and more particularly a method for controlling the hand-off for home zone services in such system.
2. Description of the Related Art
Generally, a cellular radio system provides communication service for mobile subscribers by dividing a geographical area into several, smaller, contiguous radio coverage areas called “cells”, which are served by a series of fixed radio stations called “base stations.” The base stations are connected to and controlled by a mobile service switching center (MSC). In this case, the term, “hand-off” means the process of enabling a mobile station (MS) to continue the existing mobile communication when the MS moves from one cell to another.
Referring to FIG. 1, a conventional cellular mobile telecommunications network comprises a plurality of base transceiver stations (BTS) 121 to 124 providing mobile telecommunication services to the MS 110, a base station controller (BSC) 130 for controlling the BTSs and the hand-off, an MSC 140 for connecting the BSC 130 to another BTS or PSTN (Public Switched Telephone Network), and a location registration system (LRS) 142 for storing the subscribers' information of all MSs registered in the mobile telecommunications system.
Meanwhile, a wireless local loop (WLL) connects the wireline telephone subscribers with the switching system by means of a wireless communications link in order to provide telephone services in areas where the wire lines for the PSTN may not be properly installed. Although the WLL is similar to the mobile telecommunications network in this respect, it does not provide mobile services such as hand-off but provides the wireline telephone services. Generally, the PSTN and the WLL are called “fixed network” while the cellular system and the personal communications system are called “mobile network.” The fixed network is more advantageous in sound quality but may be used only in the region limited by the “home zone.”
The concept of the home zone has been introduced in order to enable the mobile subscriber to utilize the MS as a cordless phone while traveling within a certain geographic location. If the mobile subscriber makes a call within his or her home zone, the MS functions as a conventional cordless phone and the mobile subscriber is not charged for the air time. Accordingly, within his or her home zone, the mobile subscriber can utilize the MS to originate outgoing calls without incurring expensive air time charges and without physically using a different telephone terminal, e.g., a wireline terminal such as a cordless phone. However, the conventional home zone service does not provide for the hand-off, so that the presently connected call is dropped when an MS registered for both the mobile network and the fixed network is travelling between the home zone and other regions. Hence, after completing the movement into a different region, the MS must make an attempt to reconnect the dropped call.